When machining a work-piece it is often desirable to align the machine in accordance with a target orientation in relation to the work-piece. By way of example, when drilling holes in a work-piece, it is often desirable for a hole to be drilled perpendicular to the surface of the work-piece. For example, if the finished hole is to be formed through two or more components, which are then to be fastened together with a fastener, such as a bolt, and the hole is not perpendicular to the surface, then a fastener subsequently inserted in the hole will not seat properly and the joint so formed will not be as strong as that formed by a fastener in a perpendicular hole. Additionally, when drilling through from one side to the other of a work-piece, if the hole is not normal to the surface, then the drill may emerge from the reverse side of the work-piece in an incorrect location.
It is known to be unusual, even for skilled drill operators, to be able to drill holes repeatedly and consistently to the desired standard of accuracy using manually operated hand-held drills. The required accuracy is even more difficult to achieve where access to the drilling location is restricted, as frequently happens in a production-line environment or in a domestic environment. Where access to the drilling location is particularly restricted, for example inside a small box-like structure where there is not enough space for a normal drilling tool to be held approximately perpendicular to the work-piece surface, a drilling tool with a 90° drive may be employed. When using this tool, the operator holds the main drill body approximately parallel to the work-piece surface and a gearbox on the end of the main drill body transfers the rotary drive through 90° so that the drilling axis is perpendicular to the work-piece surface. Operators find it very difficult to drill holes perpendicular to the work-piece surface using this sort of tool where they cannot sight directly along the drilling axis.
The desirability to align accurately a hand-held tool relative to a work-piece is not of course restricted to drills. In the aerospace manufacturing industry, other hand-held machines need to be so accurately aligned. By way of example, cold-working tools, which are used to expand drilled holes in metal components by a small amount to give added fatigue resistance to the component containing the hole, need to be properly aligned with the previously drilled hole. The cold-working gun is used by: (i) placing the jaw of the tool against the work-piece surface over the hole to be worked, with the axis of the tool held perpendicular to the surface, (ii) inserting an oversize mandrel through the hole and into the jaw of the tool; and (iii) the tool then pulling the mandrel through the hole, thus expanding the walls of the hole outwards. If the axis of the tool is inclined relative to the surface, rather than being held perpendicular, then the mandrel may be damaged or broken and the work-piece may also be damaged, thus incurring extra costs for tooling, rectification or scrapping.
The inconsistency of accuracy that can occur in a production situation because of the aforementioned problems can result in a high cost for re-work, or for scrapping, of incorrectly-machined components. Alignment devices for use with hand-held power tools would also be of assistance to trades-people, such as professional builders, carpenters and plumbers for example, and to DIY enthusiasts. Various alignment devices for hand-held tools such as drills are already known, but they can be bulky and unsuitable for use in confined spaces. Also, many of the prior art alignment devices require the use of separate distinct parts to function, are inflexible, provide only limited assistance to the user, are cumbersome, are complicated to use, and/or rely on a complicated array of mechanical parts that are prone to wear and possible malfunction.
It is an object of the present invention to provide an improved alignment device and/or to provide an alignment device that mitigates one or more of the above-mentioned potential disadvantages of the prior art devices and/or to provide an alignment device that is compact and simple to use, particularly for operations on production lines where repeatability of processes to high standards of accuracy is important.